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Page 1: Electrical Machines Lab-II Manual

ELECTRICAL MACHINES LAB-II

LOAD TEST ON 3-Ø INDUCTION MOTOR

LOAD TEST ON 3-Ø INDUCTION MOTOR

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ELECTRICAL MACHINES LAB-II

Aim:To conduct load test on the given 3-Φ induction motor and to plot its performance

characteristics.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 3- Ø Variac 415V/(0-470)V - 12 Ammeter (0-10)A MI 13 Voltmeter (0-600)V MI 14 Wattmeter 600V/10A UPF 25 Tachometer (0-9999)rpm Digital 16 Connecting Wires - - Required Some

Circuit Diagram:

Precautions:1. 3-Ø Variac should be in minimum position.

Procedure:1. Connect the circuit as shown in circuit diagram.2. Observing the precautions close the TPST Switch and switch ON 440V A.C supply.3. Apply the rated voltage to the stator windings of 3-Ø Induction Motor with the help of 3-Φ

Auto-transformer.4. Note down the readings of wattmeter, ammeter and voltmeter on no-load.5. Load the Induction Motor in steps using the brake-drum arrangement. At each step note down

the readings of all meters, speed and spring balance readings till full load current.6. Stop the motor by gradually releasing the load.7. Observing the precautions switch OFF the supply.

Tabular Column:

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S. No.

VL

(V)IL

(A)

WattmeterReadings (W) N

(rpm)

Spring Balance Reading %Slip Power

FactorTorque(N-m)

Output(W)

ŋ(%)W1

(W)W2

(W) S1 S2 S1~S2

1234

Formulae:Torque, Tsh = 9.81 (S1 ~ S2) R N-mInput Power, Winp = W1 + W2 WOutput Power, Wout = (2 π NTsh)/60 W%Slip = Ns – N X 100 Ns

cosØ = Wout

√3 VL IL

Efficiency = %ŋ = (Output/Input) X 100

Model Graph:

Result:

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O.C & S.C TESTS ON 1-Ø TRANSFORMER

O.C & S.C TESTS ON 1-Ø TRANSFORMER Aim:

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a) To determine the efficiency and regulation of 1- Ø transformer by conducting no-load and S.C Test.

b) To draw the equivalent circuit of 1- Ø transformer referred to L.V side as well as H.V side.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 1- Ø Variac 230V/(0-230)V, 10A - 12 1- Ø Transformer 115V/230V, 2kVA Core 1

3 Ammeter(0-10)A MI 1(0-2)A MI 1

4 Voltmeter(0-150)V MI 1(0-30)V MI 1

5 Wattmeter150V/2A LPF 175V/10A UPF 1

6 Connecting Wires - - Required Some

Circuit Diagram:O.C Test:

S.C Test:

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Precautions:1. Connections should be made tight.2. 1- Ø Variac should be in minimum position.

Procedure:1. Connect the circuit as shown in circuit diagram for O.C test.2. Observing the precautions switch ON 1- Ø A.C supply and by using the 1-Ф variac apply the rated

voltage of the primary of the transformer.3. Note down all the meter readings. Here wattmeter reading gives iron loss.4. Observing the precautions switch OFF the supply.5. Connect the circuit as shown in circuit diagram for S.C test.6. Observing the precautions switch ON 1- Ø A.C supply and by using the 1-Ф variac apply the rated

current to the transformer. (Rated power of the transformer/Voltage of primary of transformer)7. Note down all the meter readings, here wattmeter reading gives full-load copper loss.8. Observing the precautions switch OFF the supply.

Tabular Columns:O.C Test: S.C Test:

Vo (V) Io (A) Wo = W X M.F (W) VSC

(V) ISC (A) WSC = W X M.F (W)

Efficiencies at different loads and power factor:cosθ = 0.6 cosθ = 0.8

Cu Loss(W)

Output(W)

Input(W)

Efficiency(%η)

Cu Loss(W)

Output(W)

Input(W)

Efficiency(%η)

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Lagging Power Factor Leading Power Factor

Power Factor % Regulation Power Factor % Regulation

Model Calculations:Let the transformer be the step-down transformer (O.C Test)

Primary is H.V side and secondary is L.V sideRo=V1/Iw (Ω) where Iw=IocosФo

Xo=V1/Iµ (Ω) where Iw=IocosФo

Ro1=WSC/ISC2 (Ω)

ZO1=VSC/ISC

Xo1=√( ZO12 - Ro1

2)Ro2=K2 Ro1

Xo2=K2 Xo1

where,K=V2/V1=Transformation Ratio

Calculations to find efficiency:For example, at 1/4th full load,

Copper Losses=WSC x (1/4)2 (w)where, WSC=Full Load Copper Losses

Constant Losses=Wo (W)Output=(1/4) X VA X cosФ (cosФ may be assumed)Input=Output + Copper Loss + Constant LossEfficiency (%η) = (Output/Input) X 100

Efficiency at different loads and power factor can be calculated.

Model Graph:

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Result:

NO-LOAD & BLOCKED ROTOR TESTS ON 3-Ø INDUCTION

MOTOR

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NO-LOAD & BLOCKED ROTOR TESTS ON 3-Ø INDUCTION MOTORAim:

To draw the equivalent circuit of a 3- Ø Induction Motor and construct the circle diagram by conducting No-Load & Blocked Rotor Tests.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 3- Ø Variac 415V/(0-470)V - 1

2 Ammeter (0-10)A MI 1(0-5)A MC 1

3 Voltmeter(0-600)V MI 1(0-150)V MI 1(0-30)V MC 1

4 Wattmeter600V/10A LPF 2300V/10A UPF 2

5 Rheostat 100Ω/5A WW 16 Connecting Wires - - Required Some

Circuit Diagram:No-Load Test:

Blocked Rotor Test:

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To find stator resistance per phase:

Precautions:1. 3-Ø Variac should be in minimum position.

Procedure:No-Load Test:

1. Connect the circuit as shown in circuit diagram.2. Observing the precautions close the TPST Switch and switch ON 440V A.C Supply.3. Apply the rated voltage to the stator windings of 3- Ø Induction Motor with the help of 3- Ø

Auto-Transformer.4. Note down the no-load readings of wattmeter, ammeter and voltmeter.5. Bring back the auto-transformer to its minimum position and switch OFF the supply.

Blocked Rotor Test:1. Connect the circuit as shown in circuit diagram.2. Observing the precautions close the TPST Switch and switch ON 440V A.C Supply.3. By varying the variac, apply small voltage until the full load current flows in the stator windings

with the rotor unmoved.4. Note down the readings and switch OFF the supply after bringing back the auto-transformer

output to minimum position.Measurement of Stator Resistance:

1. Connect the circuit as per the circuit diagram.2. Keeping rheostat in maximum resistance position switch ON 220V D.C supply.

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3. Using Volt-Ammeter method measure the resistance of the stator winding.4. After finding the stator resistance Rdc must be multiplied with 1.6 so as to account for skin effect

i.e., Rac = 1.6Rdc

Tabular Column:Blocked Rotor Test:

Current, ISC (A) Voltage, VSC (V) W1 (W) W2 (W)

No-Load Test:Rated Voltage=

Io (A) V (V) W1 (W) W2 (W)

Stator Resistance per phase = Formulae:Go = Wo ; Yo = Io ; Bo = √(Yo

2 – Go2)

3V2 VZ01 = VSC ; R01 = WSC ; X01 = √(Z01

2 – R012)

ISC 3ISC2

For Circle Diagram:cos Øo = Wo √3 Vo Io

cos ØSC = WSC √3 VSC ISC

ISN = ISC [Vo / Vsc]

Model Graph:

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Result:

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PARALLEL OPERATION OF1- Ø TRANSFORMER

PARALLEL OPERATION OF 1- Ø TRANSFORMER Aim:

To connect two 1-Ø transformers of equal ratings in parallel and to supply study how they share a common load.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 Voltmeter(0-300)V MI 1(0-150)V MI 1

2 1- Ø Transformer 115V/230V, 2kVA Core 2

3 Ammeter (0-20)A MI 1(0-10)A MI 2

4 Resistive Load 1-Ø, 5kW Wire Wound 15 SPST Switch - Knife 16 DPST Switch - Knife 1

7 Wattmeters300V/10A UPF 2150V/20A UPF 1

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8 Connecting Wires - - Required SomeCircuit Diagram:

Precautions:1. Load should be in OFF position.2. SPST Switch is in open position.

Procedure:1. Connect the circuit as shown in circuit diagram.2. Observing the precautions switch ON the supply.3. Two readings of the voltmeter connected across switch ‘K’ is observed. If it reads zero which

means that the two secondary emf’s are opposing each other, then switch ‘K’ is closed. If it reads twice the secondary rated voltage the secondary terminals of any of the transformer are interchanged and then the switch ‘K’ is closed to make it read zero reading.

4. The load switch is closed and total load on the transformer is increased in steps. At each step, the readings of the various meters are noted down. The total load is increased till the current supplied reaches the maximum load current of both the transformers when connected parallely.

5. Observing the precautions switch OFF the supply.Tabular Columns:From S.C Test: From O.C Test:

S.No. ISC (A) Vsc (V) WSC (W) Core Loss, Wo (W) = 123

S.No. IA

(A)IB

(A)IL

(A)VL

(V)WA

(W)WB

(W)WL

(W)IA

|

(A)IB

|

(A)WA

|

(W)WB

|

(W)η

(%) % Reg

12

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3Formulae:IA

| = IL X ZB ; IB| = IL X ZA

ZA+ZB ZA+ZB

WA| = WL X ZB ; WB

| = WL X ZA ZA+ZB ZA+ZB

WSC = Isc2R ; WCu = I2R (Since I=IA

|+IB|)

ZSC = ZA = ZB = VSC / ISC

%Reg = VNL – VFL X 100 VFL

VNL = No Load VoltageVFL = Load Voltage at different loadsOutput, Wout = VL IL ; Input,Win = Wout + WCu + Wo

Efficiency, %η = Wout X 100 Win

Model Graph:

Result:

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SEPARATION OF CORE LOSSES OF 1- Ø TRANSFORMER

SEPARATION OF CORE LOSSES OF 1- Ø TRANSFORMER Aim:

To separate the core losses of a 1- Ø transformer.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 Voltmeter (0-150)V MI 12 1- Ø Transformer 115V/230V, 2kVA Core 23 Ammeter (0-2)A MC 14 DPST Switch - Knife 15 Wattmeter 300V/2A LPF 1

6 Rheostats400Ω/1.7A WW 1100Ω/5A WW 1

7 Tachometer (0-9999)rpm Digital 18 Connecting Wires - - Required Some

Circuit Diagram:

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Precautions:1. Field rheostat of the motor must be in minimum position.2. Armature rheostat of the motor must be in maximum position.

Procedure:1. Connect the circuit as shown in circuit diagram.2. Before starting the experiment, decide at which frequency you conduct No-Load test and

calculate the speed and corresponding voltage to maintain the V/f ratio constant.3. Observing the precautions switch ON the supply.4. Run the prime-mover (D.C Motor) at the required speed and adjust the level of excitation of

alternator so as to develop rated transformer primary voltage and then note down the wattmeter reading after exciting the transformer.

5. In a gradual manner, simultaneously adjust the excitation of the alternator and its speed so as to maintain a constant V/f ratio.

6. Repeat the same procedure for different frequencies.7. After completing the experiment, observing the precautions switch OFF the supply.

Tabular Columns:Tabular Column-I:

S.No. SpeedN(rpm)

Frequencyf(Hz)

VoltageV(V) V/f Wi Wi / f

12

Tabular Column-II:

S.No. Frequencyf(Hz)

Hysteresis Losses,Wi = Af (W)

Eddy Current Losses,We = Bf2 (W)

Total Iron Losses,Wi = Wh + We (W)

12

Formulae:P = 120f ; N1 = 120f1

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N PK = V = Rated Voltage f Rated frequencywhere, f = rated frequency

f1 = selected frequencyN = rated speedN1 = speed corresponding to f1

Let, Wh = Af We = Bf2

Wi = Wh + We = Af + Bf2

Wi = A + Bf fA – oa from graphB – dy = y dx xModel Graph:

Result:

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SCOTT CONNECTION OF TRANSFORMERS

SCOTT CONNECTION OF TRANSFORMERS

Aim:To convert the given 3- Ø supply into 2- Ø supply using scott connection.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 Voltmeter (0-600)V MI 2(0-300)V MI 2

2 3- Ø Variac 415V/(0-470)V - 13 Ammeter (0-10)A MI 34 Resistive Load 1-Ø, 5kW Wire Wound 25 Wattmeters 600V/10A UPF 26 Connecting Wires - - Required Some

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Circuit Diagram:

Precautions:1. 3-Ø Variac should be in minimum position.2. Load must be in OFF position.

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Procedure:1. Connect the circuit as shown in figure 1.2. Observing the precautions close the TPST Switch and switch ON 440V A.C supply.3. Apply the rated voltage to the primary of the main teaser transformer with the help of 3-Φ

Auto-transformer.4. Note down the readings of all meters for different load settings till rated full load current of the

transformer.5. Connect the secondaries of the two transformers as shown in figure 2 to verify the phase

relationship of the two phase voltages.6. Calculate the efficiency of conversion.7. Observing the precautions switch OFF 440V A.C supply.

Tabular Columns:For Figure 1: For Figure 2:

W1

(W)W2

(W)I1

(A)I2

(A)I3

(A)V1

(V)V2

(V)V3

(V)Output

(W)Input(W)

η(%)

V(V)

I(A)

V1

(V)V2

(V)

Formulae:Output = V2I2 + V3I3 (W)Input = W1 + W2 (W)Efficiency, % η = Output X100 Input

Model Graph:

Result:

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EQUIVALENT CIRCUIT OF A1- Ø INDUCTION MOTOR

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EQUIVALENT CIRCUIT OF A 1- Ø INDUCTION MOTOR Aim:

To determine the equivalent circuit parameters of a 1- Ø induction motor by conducting No-Load, Blocked Rotor and Stator Resistance Measurement Tests.Apparatus:

S. No. Name of the Equipment Range Type Quantity1 1- Ø Variac 230V/(0-230)V, 20A - 1

2 Voltmeter(0-300)V MI 1(0-150)V MI 1(0-30)V MC 1

3 Ammeter(0-10)A MI 1(0-20)A MI 1(0-5)A MC 1

4 Wattmeter300V/10A LPF 175V/20A UPF 1

5 Rheostat 100Ω/5A WW 16 Connecting Wires - - Required Some

Circuit Diagram:No-load Test:

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Blocked Rotor Test:

To find stator resistance:

Precautions:1. Initially variac must be at zero position.2. No Loose connections are allowed.3. Readings should be taken without any parallax errors.

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4. Rheostat should be in maximum resistance position.

Procedure:For No-Load Test:

1. Connect the circuit as shown in circuit diagram.2. Observing the precautions close the DPST Switch and switch ON 1- Ø A.C supply.3. Apply the rated voltage by increasing the variac output gradually (No Load is connected to the

motor).4. Note down the readings of all the meters.5. Observing the precautions switch OFF the supply.

For Blocked Rotor Test:1. Connect the circuit as shown in circuit diagram.2. For performing the blocked rotor test, block the rotor (i.e., not allowed to rotate) by applying

belt-brake arrangement and increase the voltage slowly till rated current flows and note down all the meter readings.

3. Observing the precautions switch OFF the supply.

To find Stator Resistance:1. Connect the circuit as shown in circuit diagram.2. Observing the precautions close the DPST switch and switch ON 220V D.C Supply.3. By adjusting the rheostat note down all the meter readings.4. Observing the precautions switch OFF the supply.

Tabular Columns:No-Load Test Blocked Rotor Test

Vo (V) Io (A) Wo (W) VSC (V) ISC (A) WSC (W)

To find Stator Resistance:S.No. I (A) V (V) Rs (Ω)

12

Formulae:

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Result:

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1- Ø TRANSFORMER

LOAD TEST ON 1- Ø TRANSFORMER Aim:

To determine the efficiency and regulation of a 1- Ø transformer by conducting load test.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 1- Ø Variac 230V/(0-230)V, 10A - 12 1- Ø Transformer 115V/230V, 2kVA Core 13 Ammeter (0-10)A MI 2

4 Voltmeter(0-150)V MI 1(0-300)V MI 1

5 Wattmeter 300V/10A UPF 16 Resistive Load 1-Ø, 5kW Wire Wound 17 DPST Switch - Knife 18 Connecting Wires - - Required Some

Circuit Diagram:

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Precautions:1. Connections should be made tight.2. 1- Ø Variac should be in minimum position.

Procedure:1. Connect the circuit as shown in circuit diagram.2. Observing the precautions switch ON 1- Ø A.C supply.3. Apply rated primary voltage of the transformer by properly adjusting the variac.4. Note down the readings of all the meters on No-Load.5. Switch ON the load by closing the DPST Switch and increase the load in steps and note down the

corresponding reading of all meters.6. Decrease the load on the transformer secondary and then switch OFF the supply.

Tabular Column:

InputVoltage(V)

InputCurrent(A)

InputPower(W1)

OutputVoltage(V2)

OutputCurrent(I2)

OutputPower(W2)

Efficiencyη(%)

%Regulation(%)

Formulae:Efficiency, %η = Output X100 Input%Regulation = V02 – V2 X 100 V2

Model Graph:

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Result:

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SUMPNER’S TEST

SUMPNER’S TESTAim:

i. To conduct Sumpner’s Test on two identical 1- Ø transformers.ii. To find out the iron loss, copper loss and the efficiency of each transformer.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 1- Ø Variac 230V/(0-230)V, 10A - 12 1- Ø Transformer 115V/230V, 2kVA Core 2

3 Ammeter (0-5)A MI 1(0-20)A MI 1

4 Voltmeter (0-300)V MI 2(0-75)V MI 1

5 Wattmeter 300V/5A LPF 175V/20A UPF 1

Circuit Diagram:

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Precautions:1. The range of voltmeter should be doubled the induced e.m.f of secondary winding.

Procedure:1. Connect the circuit as shown in circuit diagram.2. Connect the primaries of both transformers in parallel after ascertaining the polarities.3. Connect the secondaries in series and connect a switch as shown in the circuit diagram.4. Initially keep the switch in open circuit.5. Give supply as per the primary rating of transformers.6. Note down the readings of all the meters.7. Close the SPST Switch when voltage Vab = 0 (see circuit diagram).8. Increase the load till the full load rated current of the transformer flows by varying the auto-

transformer supplying secondaries.9. Note down the all the meter readings.

Tabular Columns:

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Vab = 0 ; Actual = Measured X F.S.DF.S.D = Full Scale Division

Load V1

(V)I1

(A)Wattmeters (W) V2

(V)I2

(A)Wattmeters (W)

Measured Actual Measured ActualNo-LoadFull-Load

For Unity Power Factor:

Load W1 (W)Iron Losses

W2 (W)Copper Losses

Total Losses Output(W)

Input(W)

Efficiencyη (%)

For 0.6 Power Factor:

Load W1 (W)Iron Losses

W2 (W)Copper Losses

Total Losses Output(W)

Input(W)

Efficiencyη (%)

Formulae:

Losses in each transformer =

η combined = X 100

Efficiency of each Transformer = η (%) = X 100

Model Graph:

Result:

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REGULATION OF 3-Φ ALTERNATOR BY

SYNCHRONOUS IMPEDANCE METHOD

REGULATION OF 3-Φ ALTERNATOR BY SYNCHRONOUS IMPEDANCE METHOD

Aim:To predetermine the regulation of a given 3-ΦAlternator by conducting O.C and S.C tests by

Synchronous Impedance Method (E.M.F Method) and MMF Method.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 Rheostats 100Ω/5A WW 1400Ω/1.7A WW 1

2 Ammeter(0-10)A MI 1(0-2)A MC 1(0-5)A MC 1

3 Voltmeter(0-300)V MI 1(0-30)V MC 1

4 Tachometer (0-9999)rpm Digital 15 Connecting Wires - - Required Some

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Circuit Diagram:

To find Armature Resistance:

Precautions:1. Field rheostat must be kept in minimum resistance position.2. Armature rheostat must be kept in maximum resistance position.3. Initially Rectifier should be in zero voltage position.

Procedure:O.C Test:

1. Connect the circuit as shown in circuit diagram.2. With the Rectifier in the zero voltage position, TPST Switch open and the rheostats in their

proper positions, the D.C Supply to the motor is switched ON.3. The D.C Motor is brought to its rated speed and thus the alternator by properly varying the

armature and/or field rheostat of the motor.4. Now, the alternator field is excited by applying the D.C voltage through the Rectifier in steps. At

each step the field current and the corresponding generated voltage are noted. This procedure is repeated till the voltage generated is much beyond rated voltage of the alternator.

5. Reduce the alternator field excitation to zero level.S.C Test:

1. With the rectifier in the minimum voltage position, the TPST Switch is closed.

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2. Increase field excitation gradually till the Short Circuit Current of the alternator reaches the rated current of the alternator.

3. Note down the field current required to circulate the rated short circuit current. Tabulate the readings taken during the O.C Test and S.C Tests.

Tabular Columns:O.C Test S.C Test

Field CurrentIf (A)

Phase Voltage(V) If(A) ISC

(A)

To find Armature Resistance:I (A) V (V) R (Ω)

E.M.F Method M.M.F MethodP.F

cosΦIa

(A)Eo (V) % Regulation P.F Field Current If (A)

Lagging Leading Lagging Leading If1 (A) If2 (A) Lagging Leading

Formulae:

for the same If and speed

[Ra = (1.3 to 1.6) Rdc ]

Generated E.M.F of alternator on No-Load is given by

‘+’ for Lagging Power Factor‘-‘ for Leading Power Factor

Percentage regulation of alternator for a given power factor is given by

(%)

where,Eo = Generated E.M.F of alternator (or excitation voltage per phase)V = Full Load rated terminal voltage per phase.

Model Graph:

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Result:

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DETERMINATION OF Xd & Xq OF SALIENT POLE SYNCHRONOUS

MACHINE

DETERMINATION OF Xd & Xq OF SALIENT POLE SYNCHRONOUS MACHINE

Aim:To determine the value of direct axis reactance (Xd) and quadrature axis reactance (Xq) of the

given synchronous machine by conducting slip test.

Apparatus:S. No. Name of the Equipment Range Type Quantity

1 3-Φ Variac 415V/(0-470)V - 12 Rheostat 400Ω/1.7A WW 13 Ammeter (0-5)A MI 14 Voltmeter (0-150)V MI 15 Tachometer (0-9999)rpm Digital 16 Connecting Wires - - Required Some

Circuit Diagram:

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Precautions:1. Connections must be made tight.2. Field rheostat must be kept in minimum resistance position.3. Starter must be in OFF position.

Procedure:1. Connect the circuit as shown in circuit diagram.2. Start the D.C Motor with the help of starter.3. Adjust the field rheostat of the D.C Motor so that it runs slightly below the synchronous speed

of synchronous machine.4. Give A.C Supply to the Alternator with the help of variac so that rated current flows in the

synchronous machine.5. The speed of D.C motor is adjusted such that the points of the meters oscillate between

maximum and minimum values.6. Note down the maximum and minimum values of ammeter and voltmeter and tabulate them.

Tabular Columns:Vmax

(V)Vmiin

(V)Imax

(A)Imin

(A)Xd

(Ω)Xq

(Ω)

Formulae:

Direct Axis Synchronous Reactance = Xd =

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ELECTRICAL MACHINES LAB-II

Quadrature Axis Synchronous Reactance = Xq =

Result:

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